1. Field of the Invention
The present invention relates to a nonvolatile semiconductor memory device having a plurality of rewritable memory blocks, and a method of controlling the same.
2. Description of the Related Art
In recent years, a flash memory that is a writable nonvolatile memory has been universally used. The flash memory is capable of retaining memory contents without being supplied with a power source. However, if erasing and writing are performed on the flash memory many times, its characteristic is deteriorated. For this reason, the number of times of data rewriting in the flash memory is limited.
Thus, there have been various proposals for enhancing reliability of the flash memory. For example, Japanese Patent Laid-Open Publication No. 2001-14865 discloses a flash memory including a rewriting number monitor. This monitor issues an alarm when the number of times of data rewriting in the flash memory exceeds a set value. Japanese Patent Laid-Open Publication No. 1992 (Hei 4)-125898 discloses an access counter for counting the number of times of access to a nonvolatile memory. When the number of times of counting reaches a predetermined value, an object to be accessed is switched to a different memory region.
However, in the proposed flash memory described above, the different memory region needs to be prepared in advance. The flash memory comprising such a memory region requires a large chip area.